Cell-cell interaction between platelets and IL-1β-stimulated vascular smooth muscle cells in synthesis of thromboxane A 2

Abstract

Transcellular biosynthesis of thromboxane (Tx) A 2 between vascular smooth muscle cells (SMC) and platelets has been investigated by using 14C-arachidonic acid (AA) radiolabeled rat SMC (or platelets) and the fate of the label in phospholipids and eicosanoid fractions was studied using radioimmunoassay (RIA) and thin-layer chromatography (TLC). Stimulation of SMC with interleukin-1β (IL-1β) resulted in production of cyclooxygenase metabolites (e.g. 6-keto-PGF 1α, PGE 2, PGF 2α, PGD 2), 15-, 11-, 5-HETE, and free AA, with a coincident decline of phosphatidylcholine (PC) in SMC. IL-1β did not induce TXB 2 production, a stable metabolite of TXA 2 measured by TLC and radioimmunoassay, either in human platelets from 0.01–100 U/ml for 1 h or in SMC for 24 h. However, human platelets converted exogenous PGH 2 to TXA 2 despite cyclooxygenase inhibition or PGH 2 receptor blockade. Furthermore, TXB 2 was produced in large quantities during co-incubation of IL-1β-stimulated SMC with human platelets for 30 min in concert with a significant decrease of 6-keto-PGF 1α and eicosanoids (PGE 2, PGF 2α and PGD 2) compared with control ( P < 0.01). Pretreatment of SMC with cycloheximide and actinomycin not only inhibited IL-1β-induced eicosanoid synthesis and phospholipid breakdown but also diminished TXB 2 production when co-incubated with platelets. These data suggest that a cell-cell interaction, i.e. platelet utilizing SMC-derived endoperoxides for its TXA 2 production, might cause an excess thromboxane A 2 synthesis.